The objective of this study is to apply genetic principles as a tool in assessing the mechanism of erythrocyte transport of amino acids and other nutrients and how such processes are regulated at the level of the genome and the effects that they have on physiological processes of the whole animal. Methods will be developed for the separation of red blood cells into various age fractions by density gradient centrifugation. The purpose of this study is to determine whether or not the previously developed high and low leucine absorbing lines of chickens differ in transport because of a difference in amount and/or kind of red blood cells present in the population of red blood cells. A randombred population of chickens will be surveyed for glycine transport in erythrocytes to determine permissible variations in transport in normal animals. Birds will be saved that have extreme low and high values for transport and these will be bred to produce the first generation high and low lines for glycine transport. Realized heritability, selection pressure, analysis of Km and Vmax of transport as well as Na-dependency will be assessed. Tests will also include analysis of blood ionic composition, leucine and lysine transport activity, egg protein content, body weight gain, etc. The mode of inheritance of the trait involved in high and low leucine transport in red blood cells will be determined. Leucine and lysine transport will be studied in vesicles of the intestinal brush border membrane of the high and low erythrocyte leucine lines. The kinetics of lysine and glycine transport in red blood cells of the leucine lines will be analyzed. The leucine lines will also be characterized for whole blood and plasma Na and K content, energy utilization, growth rate, production, reproduction, feed efficiency, body composition and mortality.